1. Field of the Invention
The present invention relates generally to a magneto-spring structure in which like magnetic poles are opposed to each other and, in particular but not exclusively, to a magneto-spring structure having a variable dynamic spring constant.
2. Description of the Related Art
Recently, technologies in connection with transportation facilities including motor vehicles have developed rapidly, and there is a demand for enhanced safety and comfortability as well as increased performance. Further, damage to the muscular and nervous systems of vehicle occupants due to exposure to vibration is becoming an issue. Symptoms of these types of damage include fatigue, vision problems or the like. Accordingly, it is important to improve the riding comfort in terms of active safety. To this end, a mechanism for reducing vibration that is inputted to the human body from vehicles is required, and various vibration models have been proposed and are put to practical use.
In recent years, accompanying the practical use of permanent magnets that have a high coercive force and high residual magnetic flux density, research is flourishing in a field such as mechanical structures and magnetic systems that utilize magnetic levitation, magnetic bearings, MR dampers, etc., which use magnetic forces and magnetic fluidity to control vibration. Because the magnetic levitation damping technology makes it possible to support physical objects with no actual physical contact, its merits include reduction of problems related to friction and wear, the capability of moving at very high speeds, and low levels of vibration and noise. Moreover, it has the advantage of being able to be used in special situations and the advantage of its force being effective in all directions. For those reasons, magnetic levitation vehicles, magnetic bearings, etc. which apply these special characteristics are being developed.
Of the levitation technologies that utilize these types of magnetic forces, the majority utilizes attractive forces. Magnetic circuits that make use of repulsive forces are difficult to utilize in vibration control systems, due to their instability, the fact that the marked non-linear characteristics of the repulsive forces are difficult to control, and their large spring constant.
In view of the above, the inventors of this application have repeated researches for practical use of a magneto-spring structure employing repulsive magnets or a suspension unit employing such a magneto-spring structure. However, in the case of the magneto-spring structures that have been researched up to this time, it has been found that the dynamic spring constant is constant independently of the amplitude of input vibration and that a structure capable of varying the dynamic spring constant depending on the input amplitude is advantageous in terms of vibration absorption.
The present invention has been developed to overcome the above-described disadvantages.
It is accordingly an objective of the present invention to provide an inexpensive and compact magneto-spring structure capable of effectively attenuating vibration input from outside by varying the dynamic spring constant.
In accomplishing the above and other objectives, the magneto-spring structure according to the present invention includes a lower frame and an upper frame vertically movably mounted on the lower frame via a link mechanism having a plurality of links. The upper and lower frames have respective permanent magnets secured thereto, with like magnetic poles opposed to each other. The magneto-spring structure also includes a connecting member for rotatably connecting the plurality of links, and a bearing in which the connecting member is inserted. The plurality of links are made of non-magnetic material, while the bearing is made of ferromagnetic material.
By this construction, magnetic flux from the permanent magnets secured to the upper and lower frames is concentrated on the bearing and increases frictional forces that act between constituent elements in the bearing. As a result, the dynamic coefficient of friction of the magneto-spring structure varies depending on input vibration, and the dynamic spring constant varies, making it possible to effectively attenuate the input vibration.
It is preferred that the connecting member be made of non-magnetic material. By so doing, the magnetic flux is concentrated on balls in the bearing, thus enabling the dynamic spring constant to vary largely.
By way of example, the magneto-spring structure according to the present invention is used for an engine mount to considerably reduce vibration inputted to a vehicle body from the engine. In this case, it is preferred that an elastic member be interposed between the upper and lower frames. The elastic member acts to further reduce the input vibration.
Advantageously, each of the permanent magnets is a two-pole magnet having two different magnetic poles on each of opposite surfaces thereof. The use of the two-pole magnets results in a compact and inexpensive magneto-spring structure, because they provide a large repulsive force when like magnetic poles are opposed to each other.